Derailleur mechanism

ABSTRACT

The supporting structure of a rear wheel derailleur mechanism for the rear wheel of a bicycle or like vehicle is connected to the carrier element for a chain guiding sprocket by an elongated link and an elongated guide. First and second pivots connect respective first longitudinal end portions of the link and guide to the supporting structure, and third and fourth pivots connect the second longitudinal end portions of the link and guide to the carrier element. A fifth pivot connects respective intersecting central portions of the link and guide. The axes of the several pivots are at least approximately parallel. The three pivots associated with the link practically prevent shifting of their pivot axes relative to the link and the connected devices, whereas the pivots at the end portions of the guide permit translatory movement of their pivot axes. A chain wheel is mounted on the carrier element for rotation in a plane transverse to the axis of rotation of the associated rear wheel, and the link and guide may be pivoted manually relative to each other about the axis of the fifth pivot.

This is a continuation of application Ser. No. 936,569 filed on Aug. 22,1978 now U.S. Pat. No. 4,231,264.

This invention relates to variable speed transmissions between the pedalcrank shaft and the rear wheel of a bicycle and like vehicle, andparticularly to a derailleur mechanism suitable for such use.

It is well known to attach a conical cluster of gear wheels to the rearwheel of a bicycle and to train a drive chain over a chain wheel on thepedal crank shaft and alternatively over the gear wheels of the clusterto achieve a desired transmission ratio. The chain is shifted betweenthe several gear wheels of the cluster by a chain wheel or guidesprocket mounted on the bicycle frame near the rear wheel shaft andshifted in the direction of the axis of rear wheel rotation by a manualcontrol device, such as a bowden cable.

In the known derailleur devices, the guide sprocket is fastened to thesupporting structure of the vehicle by a four-bar, parallelogram linkagewhose effective width in the direction of the axis of rear wheelrotation is varied by the manual control device. The conventionallinkage is relatively wide in the direction of sprocket movement so thatit projects laterally from the bicycle frame and is easily damaged inthe event of a spill. It may also snag the clothing of a careless riderduring mounting and dismounting.

A primary object of the invention is the provision of a derailleurmechanism whose linkage is narrower transversely to the direction ofnormal bicycle movement than a parallelogram linkage of comparablemechanical strength and effectiveness.

With this object and others in view, the invention provides a derailleurmechanism for the rear wheel of a vehicle whose support element may bemounted on the associated vehicle in a fixed position relative to theaxis of rotation of the vehicle wheel. Respective first longitudinal endportions of an elongated link and of an elongated guide are connected tothe support element by first and second pivots. Third and fourth pivotsrespectively connect the second longitudinal end portions of the linkand guide to a carrier element. A fifth pivot connects intermediateportions of the link and guide to each other. The axes of the fivepivots extend in a common direction. The first, third, and fifth pivotsprevent significant longitudinal movement of the link relative to thesupport element, the carrier element, and the guide. The second andfourth pivots permit longitudinal movement of the end portions of theguide relative to the respective elements. A chain wheel is mounted onthe carrier element for rotation in a plane transverse to the axis ofrotation of the vehicle wheel. A manual operating device permits thelink and guide to be moved relative to each other about the axis of thefifth pivot.

Other features, additional objects, and many of the attendant advantagesof this invention will readily be appreciated as the same becomes betterunderstood from the following detailed description of preferredembodiments when considered in connection with the appended drawing inwhich:

FIG. 1 shows a rear derailleur mechanism of the invention in simplifiedside elevation;

FIG. 2 shows the mechanism of FIG. 1 in oblique top view in thedirection of the arrow II in FIG. 1, structural elements beingrepresented by conventional symbols;

FIG. 3 illustrates the mechanism of FIG. 2 in a different operativeposition;

FIG. 4 is a side elevational view of an actual embodiment of themechanism according to FIGS. 2 and 3;

FIG. 5 shows the mechanism of FIG. 4 in oblique top view in thedirection of the arrow V, portions being broken away;

FIG. 6 shows another actual embodiment of the mechanism according toFIGS. 2 and 3 in side elevation and partially in section on the lineVI--VI in FIG. 7;

FIG. 7 illustrates the mechanism of FIG. 6 in section on the lineVI--VI;

FIG. 8 shows a modified mechanism of the invention in the manner ofFIGS. 2 and 3;

FIG. 9 shows elements of a third embodiment of the invention in a viewanalogous to that of FIG. 6; and

FIG. 10 diagrammatically illustrates the mode of operation of aderailleur mechanism of the invention in a top plan view.

Referring now to the drawing in detail, and initially to FIG. 1, thereis shown only as much of a bicycle equipped with a rear derailleurmechanism as is needed for an understanding of basic aspects of theinvention.

A bearing bracket or support element 1 is suspended from the bicycleframe by means of a mounting means or lug 25 hooked over the rear wheelshaft 3. The angular position of the lug 25 on the shaft 3 is secured bya screw 25a engaging a member of the non-illustrated rear-wheel fork ofthe bicycle frame. A conical gear cluster 4 rotates about the axis ofthe shaft 3 and is drivingly fastened to the rear wheel (not shown) forrotating the wheel when a chain 6 turns a gear in the cluster. A linkage40, yet to be described in detail, connects the bearing bracket 1 toanother bearing bracket or carrier element 7. The cage 18a of a chaintensioning and guiding device 18 is fixedly suspended from the bracketor carrier element 7 by means of a lug 7a and a shaft 18b. A leaf spring19 biases the cage 18a clockwise, as viewed in FIG. 1. The chain 6 istrained over two sprockets or chain mover elements 21, 22 in the cage18a to a gear in the cluster 4 in such a manner that the sprockets 21,22 biased by the spring 19 absorb any slack that may develop in thechain 6 when shifted from a larger gear in the cluster 4 to a smallerone by movement of the bearing bracket 7 and of the sprockets 21, 22axially of the shaft 3. Movement of the bearing bracket 7 and of theattached chain tensioning device 18 is manually controlled by operating,that is means a bowden cable 23 whose sheath or compression member 23ais secured to the bearing bracket or support element 1 by a stud 23bwhile the wire or tension member 23c in the sheath engages a movableelement of the linkage 40. Except for the linkage 40, the structuredescribed so far is analogous to the conventional type of derailleurmechanism in which the linkage 40 is replaced by a four-bar,parallelogram connection straightened by pulling the wire 23c.

The linkage 40 and associated elements of the mechanism shown in FIG. 1are represented in FIG. 2 by conventional symbols. The rear wheel shaft3 rotatably carries the five gear wheels of the cluster 4 and thebearing bracket 1 which normally is fixedly fastened to the frame andthe shaft 3. The chain 6 is trained from the sprocket 22 to the smallestgear wheel or chain wheel 4a in the illustrated position of the chainguiding device 18.

An elongated link member or link 2, which is a two-armed lever and anelongated guide member or guide bar 5 are the principal elements of thelinkage 40. The end of one of the two longitudinal end portions or equalarms of the link member or link 2 is attached to the near end of thebearing bracket 1 by a pivot 8 whose axis is perpendicular to the planeA--A indicated in FIG. 1 and fixed relative to the bearing bracket orsupport element 1 except for manufacturing tolerances. The other endportion or arm of the link 2 is similarly attached to the bearingbracket 7 by a pivot 9. Another pivot 12 provides a central fulcrum forthe link member or link 2 on the center of the guide member or guide bar5. Slots 28, 29 in the ends of the bearing brackets 7, 1 remote from thefulcrum 12 are open in opposite directions away from each other toreceive hinge pins 16, 17 on respective ends of the guide bar, thusproviding the guide bar with two sliding bearings 14, 15 which permitmovement relative to the brackets 7, 1 in the direction of elongation ofthe bar 5 as well as angular movement.

The pivoting movement of the guide bar 5 parallel to the plane A--A islimited by two abutments 24a, 24b on the bearing bracket 1. The bar 5 isengaged with the abutment 24a, as is shown in FIG. 1, by the tension ofthe bowden wire 23c against the biasing force of a return spring 27,represented in FIG. 2 by a helical wire spring tensioned betweenfasteners 27a, 27b on the link 2 and the bar 5 respectively. When thewire 23c is relaxed, the spring 27 moves the linkage 40 toward theposition of FIG. 3 in which the bar 5 engages the abutment 24b, and thesprocket 22 is aligned with the largest gear wheel or chain wheel 4e inthe cluster 4, other gear wheels or chain wheels receiving the chain 6in positions of the linkage 40 intermediate those of FIGS. 2 and 3.

As will become evident hereinafter, the tension spring 27 may bereplaced by a torsion spring at the fulcrum 12 or at the pivots 8, 9.The dimensional changes in the spring, as is shown in FIGS. 2 and 3 forthe spring 27, are quite small over the full range of movement of thelinkage 40. Therefore, the resistance of the spring to deformation bythe bowden cable 23 remains fairly uniform, a desirable feature.

The width of the linkage 40 axially of the shaft 3 is small, and thederailleur mechanisms of the invention project laterally from thebicycle frame only a very short distance, smaller than the correspondingdimension of the conventional parallelogram linkages. The probability ofdamage to the mechanism in the event of a spill is thus reduced, andsnagging of the rider's clothing is less likely.

In derailleur mechanisms of the invention based on the featuresillustrated in FIGS. 2 and 3, the chain guiding device 18 is moved bythe operating means or bowden cable 23 parallel to the axes of the gearcluster 4 and of the sprockets 21, 22. Precise alignment between thesprocket 22 and the respective gear wheels at the several transmissionratios can be maintained only by shifting the guiding device 18 overdistances equal to the axial spacings of the gear wheels in the cluster.This is not always desirable or even feasible, and some friction lossesand accelerated chain wear cannot be avoided if precise alignment is notachieved.

As is shown in FIG. 10, a path of the guiding device 18 shorter than thespacing of the gear wheels 4a to 4e in the cluster 4 has only minimaleffects on chain friction and chain wear if the guiding device 18 movesin a shallow arc indicated in FIG. 10 by a double arrow. The lowerstrand of the chain 6 moves from the chain wheel 41 on the pedal crankshaft over the sprockets 21, 22 to each gear in the cluster 4 in a planewhich appears as a straight line in the projected view of FIG. 10. Thechain paths indicated are achieved by superimposing a slight tiltingmovement on the axial movement of the guiding device 18 for thesprockets 21, 22 to compensate for the angle α through which the chain 6moves at the chain wheel 41 during shifting from the gear wheel or chainwheel 4a to the gear wheel or chain wheel 4e.

A modified derailleur mechanism producing the desired tilting motion ofthe bearing bracket for the sprocket wheels is illustrated in FIG. 8 bythe symbols employed in FIGS. 2 and 3, the position of the mechanism forthe lowest transmission ratio being represented by fully drawn lines,the position for highest transmission ratio from the chain wheel, notitself shown in FIG. 8, to the rear wheel being indicated in brokenlines. Elements identical with or corresponding to elements describedwith reference to FIGS. 2 and 3 are designated in FIG. 8 by referencenumerals having the same two last digits, but augmented by 100. As faras not explicitly described otherwise, the mechanism of FIG. 8 isidentical with that of FIGS. 2 and 3.

In the modified mechanism, the hinged connections 114, 115 between theguide bar 105 and the bearing brackets 101, 107 are provided byelongated slots 128, 129 in the two ends of the bar 105 which areengaged by hinge pins 116, 117 on the brackets 101, 107 respectively.The bracket 107 thereby is tilted through a small angle α in the planeA--A shown in FIG. 1, which is the plane of FIG. 8, during the fullavailable range of movement of the link 102 and the guide bar 105.

An analogous effect can be produced in an obvious manner by shifting theparallel axes of the pivots 8, 9, 12 and of the sliding bearings 14, 15in the mechanism of FIGS. 2 and 3 so that the axis of the pivot 12 isnot centered between the pivots 8, 9 and/or between the bearings 14, 15.

An actual embodiment of a derailleur mechanism of the inventionincluding the described features of FIGS. 1 to 3 and 8 is illustrated inFIGS. 4 and 5. Structural elements equivalent to those described withreference to FIGS. 1 to 3 are designated by the same reference numeralsaugmented by 200.

The derailleur mechanism proper is attached to the non-illustratedbicycle frame by a lug 225 near the rear wheel shaft 203. A bearingbracket 201 is angularly adjustable on the lug 225, but normally fixed.The bearing bracket 201 is connected with a bearing bracket 207 by alink 202 and a guide bar 205. Approximate longitudinal centers of thelink 202 and the bar 205 are pivotally connected by a pin 213 of afulcrum 212. An offset part 217 at one end of the bar 205 is slidablyand rotatably received in a longitudinally open, elongated slot 229 ofthe bearing bracket 201 to provide a sliding bearing 215. A similarbearing 214 is constituted at the other end of the bar 205 on thebearing bracket 207 where a terminal part 216 of the bracket 207 isreceived in a slot 228 of the guide bar 205, as described with referenceto FIG. 8.

A pivot 209 including a pivot pin 211 connects the bearing bracket 207with the link 202, and a pivot 208 including a pivot pin 210 connectsthe bracket 201 with the link 202. The bracket 207 carries the chainguiding and tensioning device 218 including a pivotally mounted carrierarm 220 biased by a spiral spring 219, a tensioning sprocket 221 and aguiding sprocket 222. Two set screws 224a, 224b on the bearing bracket201 limit the angular movements of the bar 205 and the link 202, and atubular stud 223b on the same bearing bracket abuttingly engages thesheath 223a of a bowden cable 223. The tension wire 223c of the cable isattached to the link 202.

The mode of operation of the embodiment of FIGS. 4 and 5 is obvious fromthe preceding description of FIGS. 1 to 3, 8, and 10.

Another actual embodiment of the invention is shown in FIGS. 6 and 7,and elements corresponding in structure and/or function to theafore-described elements in FIGS. 1 to 3 are designated by the samereference numerals augmented by 300.

A guide member 305 has the shape of an elongated vessel or casing closedin both longitudinal directions and of approximately U-shaped crosssection so that two longitudinal walls 305a, 305b bound a lateral openside of the casing 305. The cavity of the casing 305 receives twobearing brackets 301, 307 in longitudinally spaced relationship and aflat link 302. The casing 305 is pivotally connected with the bearingbrackets 301, 307 by sliding bearings 314, 315, and with the link 302 bya fulcrum 312.

The two bearing brackets 301, 307 are practically identical and theirportions remote from each other are formed with longitudinally open,elongated slots 329, 328. Pivot pins 316, 317 riveted between the casingwalls 305a, 305b are slidably and rotatably received in the slotsrespectively. Pivot pins 310, 311, 313 of pivots 308, 309, 312 aremounted at the ends and in the approximate center of the link 302 bypress fits and thereby secured axially. The link 302 is movably receivedin respective slots 342, 343 of the bearing brackets 301, 307, and thepin 310, 311 are journaled in the brackets. A spiral return spring 327is coiled about the pivot pins 312. It engages a longitudinal wall 305cof the casing 305 and a flange 302a of the link 302. A lug 325 fixedlybut adjustably attached to the bearing bracket 301 normally supports thederailleur arrangement on the bicycle frame in a manner obvious fromFIG. 1.

A carrier arm 320 is pivotally mounted on the bearing bracket 307 in amanner apparent from the analogous showing of FIGS. 1 and 4 and carriesa tensioning sprocket 321 and a guide sprocket, obscured in FIGS. 6 and7. Two set screws 324a, 324b are mounted on a flange 305d of the casing305. They abut against a non-illustrated flange of the link 302 in thetwo terminal positions of relative angular movement of the link 302 andthe casing 305. Except for the readily accessible heads of the screws324a, 324b the adjustable abutment arrangement is thus confined withinthe space required by other elements of the derailleur mechanism.

A variant of the linkage described above with reference to FIG. 6 isillustrated in FIG. 9 in a corresponding sectional view. Elementsstructurally or functionally equivalent to elements illustrated in FIGS.2 and 3 are designated by the same reference numerals augmented by 400.

The linkage seen in FIG. 9 includes a link 402 and a guide member 405which are both channels of approximately U-shaped cross section andelongated in a common direction. The flanges 402a, 402b of the link 402are closely juxtaposed to the flanges 405a, 405b of the guide member 405in whose cavity the link 402 is received. To permit bearing brackets401, 407 to be mounted in a simple manner, the longitudinal ends of theflanges 405a, 405b which project beyond the link 402 are offset towardeach other by the approximate thickness of the link flanges 402a, 402b.

Hinge pins 416, 417 are fastened by riveting between the flanges of theguide member 405 before assembly of the guide member with otherstructure of the derailleur mechanism. Pivot pins 410, 411 of the pivots408, 409 which connect the link 402 to the bearing brackets 401, 407 maybe fastened in the flanges 402a, 402b and are further secured againstaxial displacement by the flanges of the guide member 405 which envelopsthe link 402. The pivot pin 412 of a fulcrum 412 passes rotatablythrough aligned, closely fitting bores in the flanges 402a, 402b, 405a,405b and is secured axially by an enlarged head at one end, and a springclip 413a on the other end. The linkage shown in FIG. 9 is distinguishedby high rigidity of the connected link 402 and guide member 405.

As has been shown explicitly in FIGS. 4 and 5, features of the basicmechanisms diagrammatically illustrated in FIGS. 2 and 3 and in FIG. 8respectively may be interchanged or employed jointly, and othervariations and permutations will readily suggest themselves. Thus, FIG.2 shows a link 2 having two arms of equal length extending in oppositedirections from a fulcrum 12. As has been mentioned above, the arms maybe made of different length to achieve an arcuate path of movement forthe guiding mechanism 18. The links illustrated in the several figuresof the drawing are shorter than the cooperating guide members, but theopposite relationship is feasible in a suitably modified device. Thepivots 8, 9, 13 do not permit significant movement of the connectedmembers transverse to the respective pivot axes, while both angularmovement and limited radial displacement is available at the slidingbearings 14, 15. However, a sliding bearing may connect the centralportions of the link 2 and the guide bar 5 if one of the bearings 14, 15is replaced by a radially fixed pivot.

It should be understood, therefore, that the foregoing disclosurerelates only to presently preferred embodiments, and that it is intendedto cover all changes and modifications of the examples of the inventionherein chosen for the purpose of the disclosure which do not constitutedepartures from the spirit and scope of the invention set forth in theappended claims.

What is claimed is:
 1. A derailleur mechanism for a chain on a bicycleand like vehicle which chain is selectively engageable with a pluralityof chain wheels having a common axis of rotation comprising:(A) asupport element, (B) mounting means for mounting said support element onsaid vehicle in a fixed position relative to the common axis of rotationof said chain wheels, (C) an elongated link member, (D) an elongatedguide member, each of said link member and guide member including firstand second longitudinal end portions, (E) first and second pivot meansrespectively connecting said first longitudinal end portions to saidsupport element for angular movement of said link member and guidemember relative to said support element, (F) a carrier element, (G)third and fourth pivot means respectively connecting said secondlongitudinal end portions to said carrier element for angular movementof said link member and guide member relative to said carrier element,(H) fifth pivot means connecting respective crossing portions of saidlink member and guide member intermediate said first and second endportions thereof for relative angular movement of said link member andguide member,(1) said pivot means defining respective pivot axesextending in a common direction, (2) three of said pivot meanspreventing significant relative translatory movement of the connectedsaid link member and guide member and support element and carrierelement transversely of the respective pivot axes, (3) the other two ofsaid pivot means permitting said translatory movement, (I) a chain moverelement mounted on said carrier element, and (J) operating means formoving said link member and guide member relative to each other aboutthe axis of said fifth pivot means.